Insights into the Intrinsic Creation of Heterojunction-Based Ordered TiO₂Nanotubes Obtained from the One-Step Anodic Oxidation of Titanium Alloys

To gain insights into how the presence of the second metal in Ti alloys affects the morphology, crystallinity, chemical structure, and photocatalytic/photoelectrochemical activity of mixed-oxide nanotubes (TiO2-MxOy), five systems were electrochemically synthesized in a fluoride-containing ethylene glycol-based electrolyte by using Ti alloys, with 10 wt % of the second metal, as precursors. The level of self-organization and -orientation in the obtained samples followed the order: Ag < Cu < Mn < V < Co, being the Ti90Ag10_40V sample, the only presenting single Ag nanoparticles embedded in the oxide layer. The highest photocatalytic and photoelectrochemical activities were reported for the Ti90Ag10_40V sample, which can be attained to the heterojunction between the oxides, the formation of single Ag nanoparticles, and the high level of self-organization. Apparently, the intrinsic heterojunction between the oxides depends on the still-needed-to-be-estimated stability of the oxides produced during the anodization of each system.